Reflective condensing system for concentrating illumination at an aperture

ABSTRACT

The final condensing lens element, commonly used in a system for concentrating light at an aperture, is replaced by light restricting path means forming a transversely unobstructed, open ended light path. Spaced, opposed front surface mirrors define a portion of the path along which light is reflected back and forth between the mirror surfaces to emerge at the open end as a uniform flood of light. The absence of transverse surfaces avoids any collecting of dirt which would cause streaks to be printed on film printed with the concentrated light.

'ssa amzs 53a Bragg REFLECTIVE CONDENSING SYSTEM FOR CONCENTRATINGILLUMINATION AT AN APERTURE [451 June 13, 1972 3,263,070 7/1966 Hine..352/198 X 3,514,200 5/1970 Bowker ....350/96 OT 3,469,914 9/1969Thomson ..355/32 1,944,111 1/1934 Shieren ..350/96 OT FORElGN PATENTS ORAPPLICATIONS 523,097 4/1955 ltaly ..350/96 OT Primary Examiner-Samuel S.Matthews Assistant Examiner-Richard L. Moses Attorney-Albert M. Parker,C. G. Mueller, L. P. Brooks, A. L. Haffney, Jr., 1-1. Haidt and G. T.Delahunty [57] ABSTRACT The final condensing lens element, commonly usedin a system for concentrating light at an aperture, is replaced by lightrestricting path means forming a transversely unobstructed, open endedlight path. Spaced, opposed front surface mirrors define a portion ofthe path along which light is reflected back and forth between themirror surfaces to emerge at the open end as a uniform flood of light.The absence of transverse surfaces avoids any collecting of dirt whichwould cause streaks to be printed on film printed with the concentratedlight.

4 Claims, 9 Drawing Figures T 0R MM-uasc l PATENTEUJHMBM SHEET m 23.670.157

ATTORNEY SHEET 2 0F 2 INVENTOR. HERBER r E. BRA 00 ATTORNE).

REFLECTIVE CONDENSIN G SYSTEM FOR CONCENTRATING ILLUMINATION AT ANAPERTURE CROSS REFERENCE TO RELATED APPLICATION This application is aContinuation-in-Part of applicants copending application Ser. No.739,772, now abandoned filed June 25, 1968 and entitled ReflectiveCondensing System for Concentrating Illumination at an Aperture.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to an optical system for condensing light to produce auniform concentrated light beam at an aperture, and especially to animproved reflective condensing system which may be advantageously usedin printing motion picture films. 2. Description of the Prior ArtHeretofore, in optical systems utilized in apparatus such as contact orprojection printers for making continuous copies of motion picturefilms, difficulties have arisen due to particles of airborne dirtsettling on the surface of the lens, light diffusing plate, or otherelement closest to the printing aperture. This surface may be flat,convex, or concave and may generally be considered as being transverseto the light path as ,well as parallel to and close to the film passingthe printing aperture. Dust is attracted to any such transverse surfacedue to the accumulation of the electrostatic charges associated with thefrictional effects of the films riding together over the aperture.

It is practically impossible to keep the air completely free of dustparticles and this is particularly so when a principal source of theparticles is the edges of the film itself. Efforts have been made todispel the charges that collect these particles through the use of alphaparticles emitters, but besides being costly, this practice is not verysatisfactory. The presence of the particles on a surface through whichthe light beam passed near the aperture results in at least a partialblocking of the light passing through the condenser on the way to thefilm and, inasmuch as the film is moving, this blocking causescontinuous streaks to be printed in the prints being made from thenegative through which the light passes.

SUMMARY OF THE INVENTION The present invention provides a solution tothe prior art problem of streaks resulting in film being printed due todust particles on a transverse surface in the light path by a completelynovel approach to light condensing. No transverse lens, light diffusingplate or other surface upon which particles could collect is positionednear the aperture passed by the film to be printed. Instead of employinglenses, prisms and/or light diffusing plates the invention presents anopen light path between front surface mirrors. Light is introduced intothe path at an end remote from the aperture, directed thence by asuitable lens, to strike the reflective front mirror surface at anangle. The light is reflected back and forth between opposed mirrorsurfaces on opposite sides of the path as it travels toward theaperture. Since all of the introduced light does not strike the mirrorsurface at exactly the same angle, there will be a multitude of lightrays reflected along the path at different angles to emerge as anuniform flood of light at the aperture. Because of the multiplicity oflight rays passing along between the opposed mirrors of the path, andthe fact that the different rays are reflected at mutually differentangles along the path, any dust which might collect on a mirror surfacewill have no effect on he printing process. In other words the dust willnot be imaged at the film and will not obstruct the light travelingtoward the aperture so as to produce a dark spot which would cause astreak on the moving film. The effect of any single particle on anyparticular light ray will be lost in the multitude of reflections sothat a uniform flood of light illuminates the film at the aperture.

The opposed mirrors defining the portion of the path along which lightrays are reflected back and forth may be thought of as sides of a tube,although in practice only two opposed plane mirrors are preferably used.The mirrors may be positioned parallel to each other or may define atapering passage which is wider at its entrant or exit end. Frontsurface mirrors are preferably used, since with morrors which aresilvered on their backs, the light suffers refraction at the frontsurface both before and after reflection at the back surface.

Though the invention is illustrated in the accompanying drawing and willbe described from the standpoint of utilization in either contact oroptical printing of positive films from negatives, it is to beunderstood that its utilization is not necessarily so limited since itmay be employed in any optical system where the problems to be overcomeare those set forth herein.

The preferred and various other embodiments of the invention are setforth in the accompanying drawing and will be described in thedescription to follow.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of acondenser tube having a pair of parallel opposed top and bottom plateshaving interior reflective surfaces, with the sidewalls just dotted in,illustrative of path means according to the invention in the form of acondenser tube whose top and bottom surfaces only are formed to effectreflection of light between them.

FIG. 2 is another perspective view illustrating a tube having fourwalls, all of whose interior surfaces are formed as reflective surfaces.

FIG. 3 is a vertical sectional view of a simple optical system or aprinter showing the final condensing of light at the film aperture bymeans of reflection employing a light path in accordance with theinvention.

FIG. 4 is a similar view illustrating a form of light path withreflective surfaces converging toward the film aperture.

FIG, 5 is another similar view illustrating a light path with mirrorsdiverging towards the film aperture.

FIG. 6 is a schematic view illustrating the application of the inventionto a contact printer.

FIG. 7 is a similar view illustrating the application of the inventionto an optical or projection printer.

FIG. 8 is a plan view of a preferred form of condensing device accordingto the invention.

to the showing of FIG. 8 and looking toward an aperture.

DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 only the top and bottomwalls 1 and 2 are shown in solid lines and the mirrored interior surface3 of the bottom wall member 2 can be viewed in its entirety. It is to beunderstood that the under surface 4 of the top wall member 1 of the tubeis similarly formed with a surface reflector. The tube in this instancecould be completed by the use of side members 5 and 6, here shown merelyin dotted lines, joining the walls 1 and 2 together but spacing themapart in the relationship shown. The side members 5 and 6 as here shownwould not themselves have specially formed surface reflectors on theirsurfaces.

In FIG. 2, however, a complete tube generally indicated at 9 is shown.It has bottom walls 1 and 2 the same as in FIG. 1 and having the samereflective surfaces 3 and 4. Here, however, the side walls 5 and 6 haveinterior reflecting surfaces 7 and 8, so that light passed in at one endwill not only be reflected back and forth between the top and bottomsurface mirrors, but will also be reflected back and forth between themirror surfaces 7 and 8 formed on the interiors of the side walls 5 and6.

The application of the invention to so much of a printer as is necessaryto obtain an understanding of the invention is illustrated in FIG. 3Here, light from a source 19 is collected by a suitable lens 11, hereshown as a double convex lens, and refracted by this lens at variousangles as shown by the solid line 12, the dotted line 13 and the dotdash line 14. These light rays, merely illustrative of the multitudethat would emerge at various angles due to the refractive action of thelens 11, are

here shown as being introduced into the tube 9 at its entrant end 10.They travel through the tube reflected back and forth, due to theirdifferent angles of incidence and consequent equal angles of reflection,between the surfaces 3 and 4, as well as surfaces 7 and 8, until theyemerge at angles and at various positions at the end of the tube oraperture 15, to pass through a negative film 16 being fed down past theaperture 15.

It is to be understood that spaced parallel sprocket members, only one,17, of which is here illustrated, are employed for feeding the film 16past the aperture by means of their teeth 18. These sprockets are, ofcourse, spaced apart so that their teeth 18 register with theperforations running along adjacent the edges of the film strip. Suchsprockets have commonly been employed in printers where, instead of thereflective tube of the invention, condensing lenses have been positionedbetween the sprockets with the last lens of the set having an opticalsurface adjacent the film aperture 15. However, as already pointed out,such lens surface has a tendency to col lect dust particles.

Rays of light passing through and rendered generally parallel by such alens system cause streaks to be printed on the film passing continuouslyby. This is true whether it be film 20 being printed by contact printingas in FIG. 6, or film 21 being printed by optical or projection printingas in FIG. 7. It is believed to be clear from a consideration of FIG. 3,however, that no such forming of streaks as takes place with generallyparallel rays impinging on the film can take place where practically allof the rays reach the aperture at angles by the reflective action of thetube surfaces.

Even though, as in the FIG. 3 showing, some light will pass directlythrough the middle of the lens 11 and go directly to the film withoutany reflection, it will be coming from the convex surface of the lens11, and it will be intermingled with so much more light emerging fromthe reflective surfaces 1 and 2, that no likelihood of the printing ofany streaks on the film 20 or 21 exists.

Just as much, or even more, light arrives at the film aperture 15 by thereflective action of the interior surfaces of the reflective tubes thanin the use of condensing lenses, for a certain amount oflight is lost byrefraction in passing through the lenses. It is further significant, ofcourse, that in the reflective system of the invention there is nosurface lying across the light path and close to the aperture on whichstatic charges can accumulate to attract dust particles. The openreflective tube ofthe invention embodies no such surface.

A slight modified form of the invention is illustrated in FIG. 4. Herethe condensing device generally indicated at 25, is shown as havingwalls 26 and 27 inclined towards each other so that the opening at thelight entrant end 28 is larger than the opening at the film aperture 29.In this instance, like that of FIGS. 2 and 3, front surface mirrorsurfaces may be applied to the inner surface 30 of the top wall 26, andthe inner surface 31 of the bottom wall 27.

A side surface 32 is also shown. In his instance, only a single lightray 33 is shown emanating from the double convex lens 34, introducedinto the condensing device 25 and reflected therethrough. It is, ofcourse, to be understood that this showing of a single ray is forsimplicity of illustration and that the same multitude of rays willproceed from the lens 34 into the condensing device 25, as will proceedfrom the lens 11 in FIG. 3 to impinge on opposed, reflective interiorsurfaces.

FIG. 5 illustrates substantially the reverse of FIG. 4 in that in thisinstance a condensing device 35 has its top wall 36 and its bottom wall37 diverging from the entrant end 38 to the emerging end or printingaperture 39. Here, again, the emerging end 39 would be the size of theprinting aperture so that the end 38 would be smaller than the same. Thesurfaces 40 and 41 on the interior of the walls 36 and 37 are surfacemir' rors while if desired the same is true of the surfaces 42 of theone side wall shown and the opposed surface of an other optional sidewall, not here shown. Again, a ray 43 shown as emerging from a lens 44impinges on the surface 41 and is reflected back and forth between thesurfaces 41 and 40, until it emerges through the printing aperture 39.It passes thus through the negative film 16 and through the positivefilm 20 or 21, to be printed upon as the case may be, where the printeris either a contact or projection printer.

It is, of course, to be appreciated that in the showings of FIGS. 4 and5, convergence or divergence of the opposed reflection surfaces of thedevices 25 and 35 can just be with respect to the top and bottom wallsof the tube, leaving the op posed side walls parallel; or side walls maybe tapered similarly to the top and bottom walls so that device takesthe form of a tube which either narrows or widens, both vertically andhorizontally from its entrant end, 28 or 38, to its exit end 29 or 39.Also the reverse wall pattern can be followed.

FIGS. 8 and 9 show a preferred operational embodiment of a lightcondensing arrangement according to the invention in detail. Theapparatus of FIGS. 8 and 9 is generally indicated by the referencenumeral 50, and is adapted to be mounted upon a fixture 51, which isshown in a generally horizontal attitude in FIG. 9, but which wouldactually be vertically oriented in a typical installation such as thatschematically shown in FIG. 3.

The assembly has a flat disc-shaped base 52 upon which two generallysemicircular mirror support elements 53, 54 are mounted in opposedpositions to define a longitudinal channel 55 there between. FIGS. 8 and9 show two opposed mirrors 56 and 57, preferably mirrors of the frontsurface type, mounted within the channel 55. The use of front surfacemirrors avoids the problems of internal reflection, absorbtion andrefraction at the front surface which occur with ordinary mirrors havingtheir reflective surface at the back. This is particularly importantwhen the color distribution oflight is to be maintained the same afterreflection, because according to well known optical principals light atdifferent wave lengths is refracted and absorbed differently.

A pair of wedges fitted within the longitudinal channel 55, serve toposition the mirrors 56 and 57 in the desired relationship to eachother. Thus FIG. 8 shows the opposed mirrors 56 and 57 mounted so as tobe inclined toward each other in the direction of the aperture. By theselection of appropriate wedges 60 the angle at which the mirrors aremounted can be set to achieve any of the relationships shown in FIGS. 3,4 and 5. Converging inclination of the mirrors, as shown, is usuallypreferred, since such an arrangement provides more uniform illuminationat the film plane than does the use ofparallel mirrors. In accordancewith Lamberts Law, parallel mirrors would illuminate the center ofa filmframe more brightly than its edges. This effect is controlled by the useof convergent mirrors.

Since the device 50 is normally mounted in a vertical plane asschematically illustrated in FIG. 3, the several mirror-positioningelements and the mirrors 56 and 57 themselves must be secured againstdisplacement. As illustrated, a plurality of screws secure the elements53 and 54 to the base 52. The wedges 60 can be secured in place bygluing or by screws, or by some other suitable means.

Two generally arcuate elements 63 surround the curved peripheries ofthesupport elements 53 and 54, each ofthe elements 63 extending throughsomewhat less than 180. At the entrant end of the longitudinal channel55 the elements 63 have end faces 64 aligned with the flat sides of theelements 53 and 54 which define the channel 55. The faces 65 formed atthe opposite ends of the elements 63, near the aperture or exit end ofthe device 50, are preferably inclined as shown in FIG. 8.

A rotatable arcuate member 66 is mounted concentrically with andoutwardly of the elements 63. The member 66 has apertures 66a, 66b, 66c,66d and 66:? formed therethrough at radially spaced locations. Byrotation of the member 66 any of the apertures 66a-e can be brought intoalignment with the light path formed between the opposed mirrors 56 and57. The apertures 66a-e have different shapes and sizes so that byselecting a suitable one of the apertures the concentrated light beamleaving the device 50 can be limited to a desired width e.g. the size ofa frame of film to be printed. One of the apertures is preferably of asuitable size to illumine a complete film frame, another is smaller, toblock off light from a sound track, and so forth. The member 66 maysuitably be somewhat larger than a semicircle so that it can be rotatedfreely to bring any of its apertures 66a-e into position, but will notbecome dismounted from the member 63, though some other rotatablemounting system might be employed. Some means, not illustrated, isprovided for centering the selected aperture ahead of the mirrors.

As shown in FlG. 8, ends 56a and 57a of the mirrors 56 and 57respectively are located inwardly of the member 66, so that the member66 can be rotated to bring any of its apertures 66a 66e in line with thelight path defined between the mirrors 56 and 57. Preferably the mirrorends 56a and 57a are positioned close to the exit end of the light path,near the exit end of the light path formed by the device 50. Thus, inthe embodiment shown in FIG. 8 the ends 56a and 57a are located justinside the radius defining the inner side of the element 66. The mirrorends 56a and 57a are also preferably beveled for better lightdistribution at the film.

Thus the light path defined by the device 50 and its mirrors 56 and 57is completely unobstructed, and since the film to be printed will passclosely adjacent the selected aperture through the element 66, notransverse surfaces present themselves to gather dust or other particleswhich would obstruct the light passing to the film. Suitable means foradvancing the film past thecondensing device 50, close to, but not incontact with the element 66, are well known in the art.

In the preferred embodiment of the device 50, the several mountingelements 53, 54, 60, 63 and 66 for the mirrors 56 and 57 may be formedof metal or of synthetic resinous materials.

Finally it is appreciated that though light pathsrectangular in crosssection have been shown and described, other suitable cross sections canbe employed so long as they pass all the light therethrough byreflection and are shaped down to a film aperture for properlyilluminating the film.

It is believed that from the showing in the accompanying drawing andfrom the foregoing description, one skilled in the art will obtain afull understanding of the invention and will at the same time appreciatethe various modifications may be made in the same and other embodimentsmay be devised without departing from the spirit or scope of theinvention.

[claim 1. In an optical system for condensing light from a source andtransmitting the same for emergence at an aperture, means forming atransversely unobstructed open ended light path, said light path beingbounded throughout substantially the entire length of the path by onlytwo flat front surface mirrors with said surfaces in opposedrelationship whereby light directed in the entrant end of said pathagainst one of said surfaces at an angle is reflected to said other intoand then reflected back and forth between said surfaces to emerge as aconcentrated beam at the exit end of said path, means mounting saidfront surface mirrors in spaced relationship and inclined towards eachother in the direction toward the exit end of said path, meanscooperating with said mounting means for setting the angle at which themirrors are inclined toward each other to accommodate a particular lightsource, aperture means for engagement by a film at the exit end of saidpath, said aperture means being adjustable to provide apertures ofdifferent dimensions, and laterally enclosed transversely unobstructedpassage means completing said path from the adjacent ends of saidmirrors to said aperture means whereby no dirt can interfere with theeven flooding of said film by light from said path.

2. An optical system as in claim 1 and including a light source, lensmeans positioned between said light source and said entrant end andformed to transmit light directly from said source into the open end ofsaid light path between and against said opposed wall portions.

3. The optical system of claim 1 wherein the means for setting the angleat which the morrors are inclined toward each other include wedge meanson said mounting means.

4. The optical system of claim 1 wherein ends of the mirrors nearest theexit end of the light path are beveled for even light distribution atthe aperture.

1. In an optical system for condensing light from a source andtransmitting the same for emergence at an aperture, means forming atransversely unobstructed open ended light path, said light path beingbounded throughout substantially the entire length of the path by onlytwo flat front surface mirrors with said surfaces in opposedrelationship whereby light directed in the entrant end of said pathagainst one of said surfaces at an angle is reflected to said other intoand then reflected back and forth between said surfaces to emerge as aconcentrated beam at the exit end of said path, means mounting saidfront surface mirrors in spaced relationship and inclined towards eachother in the direction toward the exit end of said path, meanscooperating with said mounting means for setting the angle at which themirrors are inclined toward each other to accommodate a particular lightsource, aperture means for engagement by a film at the exit end of saidpath, said aperture means being adjustable to provide apertures ofdifferent dimensions, and laterally enclosed transversely unobstructedpassage means completing said path from the adjacent ends of saidmirrors to said aperture means whereby no dirt can interfere with theeven flooding of said film by light from said path.
 2. An optical systemas in claim 1 and including a light source, lens means positionedbetween said light source and said entrant end and formed to transmitlight directly from said source into the open end of said light pathbetween and against said opposed wall portions.
 3. The optical system ofclaim 1 wherein the means for setting the angle at which the morrors areinclined toward each other include wedge means on said mounting means.4. The optical system of claim 1 wherein ends of the mirrors nearest theexit end of the light path are beveled for even light distribution atthe aperture.